1. Field of the Invention
The present invention relates to sync patterns, and more particularly, to a method of inserting sync patterns of different lengths in modulated data and a recording medium having sync patterns produced by said method.
2. Description of the Related Art
Run length limited codes, generically designated as (d, k) codes, have been widely and successfully applied in modern magnetic and optical recording systems. Such codes, and means for implementing such codes are described by K. A. Schouhamer Immink in the book entitled “Codes for Mass Data Storage Systems” (ISBN 90-74249-23-X 1999). Run length limited codes are extensions of earlier non return to zero recording codes, where binary recorded “zeros” are represented by no (magnetic flux) change in the recording medium, while binary “ones” are represented by transitions from one direction of recorded flux to the opposite direction.
A (d, k) code must satisfy the constraints that at least d “zeros” are recorded between consecutive “ones”, and no more than k “zeros” are recorded between consecutive “ones”. In, for example, a (1, 7) code there is at least one “zero” between “recorded “ones”, and there are no more than seven recorded contiguous “zeros” between recorded “ones”.
The series of encoded bits is converted, via a modulo-2 integration operation, to a corresponding modulated signal formed by bit cells having a high or low signal value. A “one” bit is represented in the modulated signal by a change from a high to a low signal value or vice versa, and a “zero” bit is represented by the lack of change in the modulated signal.
The EFM (Eight-to-Fourteen Modulation) system used for recording information on a Compact Disk (CD) can be found in U.S. Pat. No. 4,501,000. The EFM-modulated signal is obtained by converting a series of 8-bit information words into a series of 14-bit code words.
In the meantime, the EFM+ system is used for recording information on a lately-developed high-density disk, generically called a DVD. In the EFM+ system, a series of 8-bit information words is converted into a series of 16-bit code words. An operation of a coding device adopting the EFM+ system is described below briefly.
FIG. 1 is a block diagram of a coding device which comprises a data receiver 10 receiving a series of 8-bit information words; an encoder 20 converting the received series of information words into a series of 16-bit code words, namely, channel data under a given (d, k) constraints; and a sync inserter 30 inserting a sync pattern periodically in the channel data.
The sync pattern is used for synchronizing a decoder (not shown) with a reproduced bit trains of channel data in a later reproduction. In a DVD, a sync pattern is inserted every frame, thus, total 416 sync patterns (=26 frames×16 sectors) are inserted in a 32-Kbyte ECC block containing channel data modulated by the EFM+ system, as shown in FIG. 2. The sync data is 32-bit long and has 8 different patterns to distinguish among a sector start, even or odd frame, and so on.
However, even though the sync data is essential to data decoding, it conveys no information. As a result, the insertion of sync data reduces the storage capacity of a recording medium such as DVD.